Siemens SIMATIC ET 200S, Руководство пользователя

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Digital Electronic Modules
11-5
ET 200S Distributed I/O System
EWA-4NEB 780602402-12
Pulse stretching
The pulse stretching is a function used to modify a digital input signal. A pulse at a
digital input is stretched to at least the length set in the parameters. If the input
pulse is already longer than the selected length, it is not changed
Principle of Pulse Stretching
The figure below shows a few examples of input pulse modification.
Pulse stretching parameter = T
1
Process signal
”processed”
input signal
Pulse is shorter than T
1
,
and is stretched to T
1
.
Pulse is longer than T
1
and
is thus not changed.
Process signal
”processed”
input signal
The second pulse output during active
pulse stretching is shifted until the
current stretching period has expired.
Short pulses output within a
pulse stretching cycle are
ignored.
T
1
for 0 > 1 edge
T
1
for 1 > 0 edge
Figure 11-1 Principle of Pulse Stretching
Note
If you set pulse stretching for an input channel, this also affects the flutter
monitoring enabled for this channel. The ”pulse stretched” signal is the input signal
for flutter monitoring. You should therefore adapt the pulse stretching parameters
and flutter monitoring functions to each other. Select appropriate parameter values
in order to tune the functions to your process.